This invention relates to an improved apparatus and method for uniformly coating the insides of tubular extensions.
Coating the inside of tubular extensions such as oilfield tubings has been disclosed and known in the art for quite some time. Coating with a thermal type material applied to a tubular extension which has previously been heated is used to prevent corrosion and erosion. Additionally, drill pipe is customarily coated in order to reduce friction and wear in the pipe. Pipes which have been coated require less pressure to pump fluid due to reduced friction. An example of an interior pipe coating apparatus is disclosed in Warren et al U.S. Pat. No. 4,382,421 which utilizes measured charges of fusible particles for coating the interior of pipes. Another example of a method of powder coating the inside of tubular extensions is shown in Gibson U.S. Pat. No. 4,243,699 which causes an excessive amount of material to be blown through a previously heated pipe. Various factors are combining to make these previous devices totally or partially ineffective and deficient as pipe coaters. Currently, pipe lengths are increasing. The incentive for longer pipe lengths is due to the high cost of ensuring quality joining of pipe sections. Because joints are expensive, pipe lengths have increased. The increased pipe lengths have limited the usefulness of previous inventions in this area due to the fact that these previous devices are unable to provide a uniform interior coating over an extended length. Previous devices have relied on introducing an excessive amount of coating material in order to ensure that all of the interior of the tubular extensions are coated. This procedure results in application of material to the interior of tubular extensions which is too thick at the beginning of the pipe and too thin at the opposite end.
Additionally, it is not infrequent to encounter weld splatter inside tubular extensions which are manufactured with welded seams. Some of this splatter is not removed when the pipe is cleaned prior to applying the coating. In fact, some of the splatter becomes part of the interior of the pipe. Previous methods and apparatus for applying coatings to the insides of tubular extensions are incapable of ensuring that the hills, bumps and cavities caused by weld splatter will be sufficiently covered to produce and acceptable coating.
Further, because the coating material utilized to coat the interior of these tubular extensions is expensive, and because previous systems utilize an over sufficiency of the material to ensure that the entire length of the pipe is coated, a certain portion of the material passes through the heated pipe and comes out the opposite end unattached. In prior apparatus, this material then is aded to the new material for reuse in the coating of pipes. The problem with this procedure is that the coating material which has once passed through and been heated by a pipe, even though it does not adhere to the insides of the pipe, cannot help but be affected by the heat because it is designed to be thermal sensitive. As a result, the partially heated material which has adhered, in most instances, to other particles but not to the pipe is not of a uniform size when it is mixed with the new, unused coating material. This contamination of new material with used, partially heated material adds to the problem of non-uniform coating of the interior of the tubular extensions.
A further drawback of previous devices is that they rely on the quick response of a human operator at the far end of a tubular extension to collect the excess material which is blown through the pipes. Inevitably, some of this material is blown onto the operator and into the atmosphere where it can be inhaled, thereby presenting a serious health hazard. Still another drawback of previous devices is that they were unable to ensure constant rotation speeds for variously sized pipes. These previous devices work reasonably well when the same diameter pipe is coated in many consecutive sections. But, with previous systems, each different sized diameter pipe rotates at a different speed thereby causing delay for altering speed or non-uniform rotation and application speeds if no change is made. Yet another drawback in previous devices is that no means is provided for the preparation of the bitter ends of the tubular extensions. That is, once the pipe interior is coated, it is also necessary to coat the very ends of the pipe. In previous devices this is done by hand when the pipe is rotating at very high speeds. This activity requires operators to approach a dangerously rotating pipe section for application of coating material.
Thus, there is a need in the art for providing a coating device which turns all pipe sections, no matter what their length or diameter, at a constant, predetermined speed, that does not utilize an excess amount of coating material nor introduce excess coating material into the atmosphere thereby causing a health hazard, that does not reutilize heat sensitive material which has been exposed to heat and contaminated, which avoids the problem of heavy buildup of coating material at one end and light buildup of material on the opposite end of the pipe and which provides for safe rotation of the pipe during end preparation. It, therefore, is an object of this invention to provide an improved apparatus and method for uniformly applying a coating to the interior of cleaned and heated tubular extensions.